Import bmake-20171028

From ChangeLog

2017-10-28 Simon J. Gerraty <sjg@bad.crufty.net>

• VERSION: 20171028 Merge with NetBSD make, pick up o main.c: ignore empty MAKEOBJDIR
• Makefile.config.in: make @prefix@ @machine*@ and @default_sys_path@ defaults.

2017-10-05 Simon J. Gerraty <sjg@bad.crufty.net>

• VERSION: 20171005
• unit-tests/dotwait.mk: redirect stderr through pipe for more consistent result on some platforms.

2017-08-13 Simon J. Gerraty <sjg@bad.crufty.net>

• machine.sh: entry for AIX

2017-08-12 Simon J. Gerraty <sjg@bad.crufty.net>

• VERSION (_MAKE_VERSION): Move the setting of _MAKE_VERSION to a file that can be included by configure as well as make. This allows configure to set set _MAKE_VERSION in make-bootstrap.sh

2017-08-10 Simon J. Gerraty <sjg@bad.crufty.net>

• Makefile (_MAKE_VERSION): 20170810 Merge with NetBSD make, pick up o meta.c: if target is in subdir we only need subdir name in meta_name.